In the essential fatty acid (EFA) deficient epidermal skin disease, lack of the dietary essential fatty acids 18:2 and 20:4 (n-6) results in a hyperproliferative epidermis. Topical application of 18:2 (n-6) normalizes the epidermal proliferation through an unknown mechanism. The hypothesis driving this proposal is that the fatty acid content of membrane phospholipids controls the viscosity (fluidity) of the cell membrane and that this parameter, in turn, affects membrane mechanisms that control cell function. The long-term objective of the proposed studies is to determine the mechanism of membrane phospholipid fatty acid regulation of keratinocyte function. In vitro EFA deficient keratinocytes will be grown in essential fatty acid supplemented medium to yield cells with "normalized" membranes. For the EFA deficient cells, the "normalization" of their phospholipid fatty acid content and successful measurements of membrane viscosity have been reported by us. Thus it is proposed to use this characterized keratinocyte culture in Electron Paramagnetic Resonance experiments, with concomitant High Performance Liquid Chromatography and Gas Chromatographic analysis and extensive data reductions to: 1) Discover the key determiners of membrane viscosity and membrane fatty acid profile; 2) Test the effect of different membrane fatty acid compositions on enzyme kinetic rates of fatty acid elongation/shortening and saturation/desaturation; 3) Discover and monitor the pathways for the products of the arachidonic acid cascade that are important to health and integrity. Performance of the proposed studies will identify mechanisms by which the membrane fluidity of the cells alters the activity of membrane- associated enzyme and signal transduction systems. Understanding these basic mechanisms will expand our knowledge of epidermal function and diseases.